|Publication number||US5208546 A|
|Application number||US 07/748,136|
|Publication date||May 4, 1993|
|Filing date||Aug 21, 1991|
|Priority date||Aug 21, 1991|
|Also published as||EP0528651A2, EP0528651A3|
|Publication number||07748136, 748136, US 5208546 A, US 5208546A, US-A-5208546, US5208546 A, US5208546A|
|Inventors||Krishnaswamy Nagaraj, Reza S. Shariatdoust|
|Original Assignee||At&T Bell Laboratories|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Non-Patent Citations (2), Referenced by (56), Classifications (15), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to phase-locked loops and more specifically to charge pumps for phase-locked loops.
A basic phase-locked loop (PLL) is a circuit which produces an output signal synchronized to an input reference signal. A PLL output signal is synchronized or "locked" to a reference signal when the frequency of the output signal is the same as that of the reference signal. Under locked conditions, a PLL may provide for a constant phase difference between the reference and output signals. This phase difference may assume any desired value including zero. Should a deviation in the desired phase difference of such signals develop (i.e., should a phase error develop) due to, e.g., variation in either (i) the frequency of the reference signal or (ii) programmable parameters of the PLL, the PLL will attempt to adjust the frequency of its output signal to drive the phase error toward zero.
There are several different types of PLLs. Among these are PLLs which are charge pump-based. In a charge pump-based PLL, a phase-frequency detector compares an input reference signal to an output signal from a voltage controlled oscillator for the purpose of observing phase and frequency differences between the signals. If differences are observed, the phase-frequency detector produces logic pulses indicative of such differences. A charge pump receives these logic pulses and, based thereon, provides pulses of current to a loop filter and ultimately the voltage controlled oscillator. As filtered, these current pulses serve to adjust the voltage controlled oscillator to compensate for the observed differences.
The magnitude of PLL bandwidth is a parameter affecting PLL performance. The larger the bandwidth, the larger the steady-state phase jitter (i.e., the larger the phase error due to circuit noise) of the PLL but the smaller the settling time for variations in the reference signal or PLL parameters (i.e., the smaller the time needed by the PLL to adjust to the variations). The smaller the PLL bandwidth, the smaller the steady-state phase jitter, but the larger the settling time. Consequently, a PLL design trade-off issue can exist between desirable values of steady-state phase jitter and reference signal/PLL parameter variation settling time.
The present invention provides a method and apparatus for temporarily providing an increased PLL bandwidth responsive to variations or transients in a reference signal or programmable loop parameters, and a narrow bandwidth during the steady-state.
An illustrative embodiment of the present invention comprises an adaptive charge pump which operates to employ a relationship between the magnitude of charge pump current and PLL bandwidth. This relationship provides that increases in charge pump current tend to increase PLL bandwidth, while decreases in current tend to decrease PLL bandwidth. The embodiment provides for sensing the above-described variations and, responsive thereto, temporarily increasing the magnitude of charge pump current. The increased charge pump current increases PLL bandwidth and therefore decreases settling time of a PLL in response to such variations. Once PLL output signal phase has been modified to track the variations, the charge pump current is reduced, reducing PLL bandwidth and steady-state phase jitter. The temporary nature of an increase in charge pump current provides for enhanced PLL settling properties, as needed, without a sustained increase in PLL steady-state phase jitter.
The illustrative embodiment of the present invention functions by operation of a variation sensor in combination with a variable current source. The variation sensor monitors the outputs of a PLL's phase-frequency detector for the presence of logic pulses indicating a variation to be tracked. Responsive to sensing significant logic pulses, the variation sensor signals the variable current source that increased current should be provided to the loop filter and VCO of the PLL to improve settling time. The variable current source responds by increasing the magnitude of its output current pulses, thereby increasing PLL bandwidth and providing for quicker adjustment to the sensed variation.
Once the voltage controlled oscillator of the PLL responds to the filtered current pulses by adjusting its output to track the variation, significant logic pulses from the phase-frequency detector cease. The variation sensor responds to the lack of significant logic pulses by de-asserting its signal to the variable current source, which, in response, reduces the magnitude of current pulses it produces.
The present invention has use in many systems such as clock signal synthesizer systems for, among other things, video graphics applications.
FIG. 1 presents an illustrative charge pump-based phase-locked loop.
FIG. 2 presents an illustrative embodiment of the adaptive charge pump of the present invention.
FIG. 3 presents an illustrative variation sensor.
FIG. 4 presents an illustrative variable current source.
An illustrative charge pump-based phase-locked loop (PLL) 50 is presented in FIG. 1. A reference signal UI is received by a digital programmable divider circuit 75, which divides the frequency of UI by a programmable value N. A resulting signal, UIN, is provided to a phase-frequency detector (PFD) 100. Also provided to the PFD 100 is signal UOM, which is the output of a voltage controlled oscillator (VCO) 400, UO, divided by a number M by another digital programmable divider circuit 500. PFD 100 detects differences in phase and frequency between UIN and UOM, and provides logic signals to an embodiment of an adaptive charge pump 200 indicating when such differences have been detected. By arbitrary convention these logic signals are designated as DOWN and UP, respectively. (It will be apparent to one of ordinary skill in the art that the opposite convention could be chosen.)
The adaptive charge pump 200 is coupled to a loop filter 300 and provides a charge pump output current, ICO, to the loop filter 300 based on the received UP/DOWN logic signals. The loop filter 300 provides low-pass filtering to ICO, yielding a filtered signal UF. This signal is provided as feed-back to the VCO 400.
The digital programmable dividers 75 and 500 in the illustrative embodiment may be any of those well known in the art. The illustrative PFD 100 may be any of the well-known types, such as that presented in FIG. 6.18 in F. M. Gardener, Phaselock Techniques, 123-25 (1979). The loop filter 300 of the illustrative embodiment is a first order low-pass filter. The illustrative VCO 400 comprises a voltage to current converter coupled to a ring oscillator which comprises three current controlled inverters.
The illustrative embodiment of the adaptive charge pump 200 is presented in FIG. 2. UP/DOWN logic signals from PFD 100 are provided to both a variation sensor (VS) 220 and a variable current source (VCS) 260. The VS 220 is coupled to VCS 260, and both are coupled to a power supply voltage, VDD. Responsive to detecting significant UP/DOWN logic signals from the phase-frequency detector 100, the VS 220 sends a variation signal, U'VS, to the VCS 260. The VCS 260 provides output current ICO to the loop filter 300 of the PLL 50.
An illustrative VS 220 is presented in FIG. 3. As shown in the Figure, the UP/DOWN logic signals from the PFD 100 are logically ORed by gate 225 to form signal S1. Signal S1 controls the operation of a switch 229, which in turn modulates the flow of current, I1, from current source 227. Switch 229 will close during the intervals when signal S1 is logically true. Resistor 235 is coupled to switch 229 at node A, along with current source 233. Capacitor 231 is coupled to resistor 235 at node B.
Current source 233 provides a current I2 which is related to current I1 as follows: ##EQU1## where n is, for example, 10. The value of n determines the average duty cycle of S1 deemed to be significant so as to cause an increase in VCS 260 output current. For example, for I1 =20 μA and I2 =2 μA (n=10), UP/DOWN logic pulses causing a duty cycle for S1 >0.1 (i.e., greater than 10 percent) will be deemed significant for purposes of variation sensing. (see, section entitled Operation of the Illustrative Embodiment).
The voltage signal at node B is designated as UVS. This signal is received by inverter 237 which provides as output a logical TRUE signal whenever it receives an input signal which is less than or equal to a threshold, Vth. Inverter 237 will provide as output a logical FALSE signal whenever it receives an input signal which is greater than Vth. Because of this threshold, the inverted signal output from inverter 237 is indicated with a "prime" notation: U'VS. This output is again inverted by inverter 239 to provide signal U'VS. It is this signal, U'VS, which is output to the VCS 260.
An illustrative variable current source 260 is presented in FIG. 4. As shown in the Figure, the VCS 260 includes two current sources, 265 and 275, which are directly modulated by the UP and DOWN logic pulse signals from the PFD 100 by operation of switches 290 and 292, respectively. VCS 260 also includes two current sources 270 and 280 which are modulated not only by the UP and DOWN logic pulse signals applied to switches 290 and 292, respectively, but also by signal U'VS, by operation of switches 285 and 287, respectively. Exemplary values for I3 and I4 are 4 μA and 20 μA, respectively.
When signal U'VS is logically FALSE, the output current of the VCS 260, ICO, may comprise current from either of sources 265 or 275, depending on the presence or absence of UP or DOWN logic pulse signals controlling switches 290 or 292, respectively. However, when signal U'VS is logically TRUE, the output current of the VCS 260 may comprise current from either of sources 265 or 275, depending on the presence or absence of UP or DOWN logic pulse signals, plus current from either source 270 or 280.
In light of the above, it will be understood by one of ordinary skill in the art that current sources controlled by switches in the VCS 260 and the VS 220 may comprise separate switches and sources, as presented in FIGS. 3 and 4, or unified switched current sources. Whether separate or together as a single element, such may be formed with field effect transistors using techniques well known in the art.
Under steady-state (e.g., locked) conditions, the UP/DOWN logic signals from PFD 100 are infrequent and of short duration, if present at all. As a result, the duty cycle, DS, of signal S1 from OR gate 225 is very small or zero (e.g., less than 10 percent). Switch 229 will therefore remain open most of the time and current source 227 will be largely blocked. (Under steady-state conditions, some conventional PFDs provide narrow UP/DOWN spikes from time to time; as will be appreciated by the ordinary artisan, these spikes will not affect the fundamental operation of this embodiment.) At the same time, current source 233 is working to pull charge from capacitor 231 via resistor 235 at a rate of I2 =I1 /n. Since I2 >I1 ×DS, the voltage across the capacitor, UVS, is driven toward zero. The condition of UVS ≦Vth is sensed by the threshold logic of inverter 237, causing it to output a logical TRUE signal. In response, inverter 239 provides a logical FALSE signal, U'VS, to switches 285 and 287 of VCS 260. This FALSE signal causes the switches to open (or allows them to remain open). VCS 260 output current, ICO, is therefore equal to I3, as provided by current source 265 or 275, when switch 290 or 292, respectively, is closed.
As a result of significant variations in the reference signal UI, or in the programmable values of M and N (e.g., resulting in loss of lock), significant UP/DOWN logic pulse signals are produced. Accordingly, the duty cycle, DS, of signal S1 is large (e.g., greater than 10 percent). Switch 229 will close whenever signal S1 is TRUE. Each time switch 229 closes, current I1 is allowed to flow and, as a result, charge is deposited on capacitor 231. If the current I1 ×DS (the rate at which charge is being deposited on the capacitor) exceeds the current I2 (the rate at which charge is being drained from the capacitor), the voltage at node B, UVS, will be driven toward the supply voltage, VDD. The condition of UVS >Vth is sensed by the threshold logic of inverter 237, causing inverter 237 to output a logical FALSE signal. In response, inverter 239 provides a logical TRUE signal, U'VS, to switches 285 and 287 which close in response. During the time when switches 285 and 287 are closed and UP/DOWN pulses are present, VCS 260 output current, ICO, is equal to I3, as provided by current source 265 or 275, plus I4, as provided by current source 270 or 280. Responsive to increased output current, ICO, the bandwidth of the PLL 50 is increased thus enhancing its variation settling properties.
As a result of the VCO 400 adjusting its output signal to reduce the PLL 50 phase error (between signal UIN and output signal UOM) to a small, if not zero, level, the PFD 100 will cease generating significant UP/DOWN logic pulses. Absent such significant logic pulses, the voltage at node B of the VCS 260, UVS, is driven toward zero by current source 233. The condition of UVS ≧Vth is sensed by the threshold logic of inverter 237 causing it to provide a logical TRUE signal as output. This signal is inverted by inverter 239 to a logical FALSE signal causing switches 285 and 287 to open. As a result, VCS 260 may provide output current equal to I3 from sources 265 and 275, depending on the presence of UP/DOWN logic pulses at switches 290 and 292, respectively. Responsive to this level of output current, the PLL 50 exhibits a reduced level of phase jitter compared with that exhibited by the PLL 50 when its output current equals the sum of I3 and I4.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3610954 *||Nov 12, 1970||Oct 5, 1971||Motorola Inc||Phase comparator using logic gates|
|US4524333 *||Aug 11, 1982||Jun 18, 1985||Nippon Telegraph & Telephone Public Corporation||Phase-locked loop using integrated switched filter|
|US4885554 *||Dec 16, 1988||Dec 5, 1989||Tektronix, Inc.||Phase-offset signal generator|
|US4890072 *||Feb 3, 1988||Dec 26, 1989||Motorola, Inc.||Phase locked loop having a fast lock current reduction and clamping circuit|
|US4920320 *||Dec 19, 1988||Apr 24, 1990||Motorola, Inc.||Phase locked loop with optimally controlled bandwidth|
|1||*||F. M. Gardener, Phaselock Techniques, 123 25 (1979).|
|2||F. M. Gardener, Phaselock Techniques, 123-25 (1979).|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5315269 *||Jul 31, 1992||May 24, 1994||Nec Corporation||Phase-locked loop|
|US5357215 *||May 14, 1993||Oct 18, 1994||Siemens Aktiengesellschaft||Method of setting phase locked loops by comparing output signals in a phase detector|
|US5384550 *||Sep 18, 1992||Jan 24, 1995||Rockwell International Corporation||Loop transient response estimator for improved acquisition performance|
|US5414745 *||Jun 1, 1993||May 9, 1995||Advanced Micro Devices, Inc.||Synchronized clocking disable and enable circuit|
|US5432481 *||Nov 17, 1994||Jul 11, 1995||Kabushiki Kaisha Toshiba||Phase-locked loop circuit|
|US5448598 *||Jul 6, 1993||Sep 5, 1995||Standard Microsystems Corporation||Analog PLL clock recovery circuit and a LAN transceiver employing the same|
|US5479458 *||Oct 5, 1994||Dec 26, 1995||Tanaka; Yoshiaki||Digital phase shifter including 1/N for phase detect and subsequent VCO adjust|
|US5491439 *||Aug 31, 1994||Feb 13, 1996||International Business Machines Corporation||Method and apparatus for reducing jitter in a phase locked loop circuit|
|US5495207 *||Aug 31, 1994||Feb 27, 1996||International Business Machines Corporation||Differential current controlled oscillator with variable load|
|US5513225 *||Aug 31, 1994||Apr 30, 1996||International Business Machines Corporation||Resistorless phase locked loop circuit employing direct current injection|
|US5525932 *||Aug 31, 1994||Jun 11, 1996||International Business Machines Corporation||Lock indicator for phase locked loop circuit|
|US5546052 *||Nov 10, 1994||Aug 13, 1996||International Business Machines Corporation||Phase locked loop circuit with phase/frequency detector which eliminates dead zones|
|US5561390 *||Oct 27, 1994||Oct 1, 1996||Nec Corporation||Clock signal generation circuit having detective circuit detecting loss of reference clock|
|US5619161 *||Mar 5, 1996||Apr 8, 1997||International Business Machines Corporation||Diffrential charge pump with integrated common mode control|
|US5646563 *||Sep 30, 1996||Jul 8, 1997||National Semiconductor Corporation||Charge pump with near zero offset current|
|US5646564 *||Apr 12, 1996||Jul 8, 1997||Xilinx, Inc.||Phase-locked delay loop for clock correction|
|US5663689 *||Jun 26, 1996||Sep 2, 1997||International Business Machines Corporation||Method and apparatus for providing a high speed charge pump with low static error|
|US5694062 *||Feb 2, 1996||Dec 2, 1997||Lsi Logic Corporation||Self-timed phase detector and method|
|US5703511 *||Oct 23, 1996||Dec 30, 1997||Fujitsu Limited||Charge pump circuit, PLL circuit with charge pump circuit, and semiconductor integrated circuit with charge pump circuit|
|US5703539 *||Dec 17, 1993||Dec 30, 1997||Motorola, Inc.||Apparatus and method for controlling the loop bandwidth of a phase locked loop|
|US5805002 *||Aug 22, 1996||Sep 8, 1998||Ic Works, Inc.||Slow transition time phase frequency detector and method|
|US5808494 *||Aug 27, 1996||Sep 15, 1998||International Business Machines Corporation||Apparatus and method for generating a clock in a microprocessor|
|US5815016 *||Jun 14, 1996||Sep 29, 1998||Xilinx, Inc.||Phase-locked delay loop for clock correction|
|US5831484 *||Mar 18, 1997||Nov 3, 1998||International Business Machines Corporation||Differential charge pump for phase locked loop circuits|
|US5886551 *||Mar 25, 1997||Mar 23, 1999||Nec Corporation||Charge pump circuit for use in a phase locked loop|
|US5898328 *||Apr 10, 1997||Apr 27, 1999||Sony Corporation||PLL circuit having a switched charge pump for charging a loop filter up or down and signal processing apparatus using the same|
|US5929678 *||Sep 3, 1997||Jul 27, 1999||U.S. Philips Corporation||Frequency synthesis circuit having a charge pump|
|US6002273 *||Oct 5, 1998||Dec 14, 1999||Motorola, Inc.||Linear low noise phase-frequency detector|
|US6226339 *||Oct 7, 1997||May 1, 2001||Samsung Electronics Co., Ltd.||Method and system for detecting phase lock in a phase-locked loop|
|US6288602 *||Dec 29, 1995||Sep 11, 2001||International Business Machines Corporation||CMOS on-chip precision voltage reference scheme|
|US6327319||Nov 6, 1998||Dec 4, 2001||Motorola, Inc.||Phase detector with frequency steering|
|US6456165||Aug 18, 2000||Sep 24, 2002||International Business Machines Corporation||Phase error control for phase-locked loops|
|US6608510 *||Mar 30, 2001||Aug 19, 2003||Hitachi, Ltd.||PLL circuit and wireless mobile station with that PLL circuit|
|US6614318 *||Nov 5, 2001||Sep 2, 2003||Xilinx, Inc.||Voltage controlled oscillator with jitter correction|
|US6657917 *||Jul 2, 2001||Dec 2, 2003||Micron Technology, Inc.||Selective adjustment of voltage controlled oscillator gain in a phase-locked loop|
|US6806742 *||May 23, 2003||Oct 19, 2004||Standard Microsystems Corporation||Phase detector for low power applications|
|US6812754 *||Jun 5, 2000||Nov 2, 2004||Renesas Technology Corp.||Clock synchronizer with offset prevention function against variation of output potential of loop filter|
|US6876185 *||Jun 3, 2003||Apr 5, 2005||Fujitsu Limited||PLL semiconductor device with testability, and method and apparatus for testing same|
|US6912380 *||Mar 29, 2001||Jun 28, 2005||Renesas Technology Corp.||PLL circuit and wireless mobile station with that PLL circuit|
|US6989699 *||Jan 29, 2004||Jan 24, 2006||Infineon Technologies Ag||Phase detection circuit having a substantially linear characteristic curve|
|US7062004 *||Jul 13, 2001||Jun 13, 2006||Silicon Image, Inc.||Method and apparatus for adaptive control of PLL loop bandwidth|
|US7570105 *||Oct 4, 2007||Aug 4, 2009||Altera Corporation||Variable current charge pump with modular switch circuit|
|US7622967 *||Sep 19, 2007||Nov 24, 2009||Nec Electronics Corporation||Phase shifting circuit having a constant phase shift|
|US8089307 *||Mar 4, 2009||Jan 3, 2012||Cambridge Silicon Radio Limited||Charge transfer in a phase-locked loop|
|US20020086652 *||Mar 29, 2001||Jul 4, 2002||Taizo Yamawaki||PLL circuit and wireless mobile station with that PLL circuit|
|US20030001679 *||Jul 2, 2001||Jan 2, 2003||Lever Andrew M.||Sub-ranging wide-bandwidth low noise PLL architecture|
|US20030201786 *||Jun 3, 2003||Oct 30, 2003||Fujitsu Limited||PLL semiconductor device with testability, and method and apparatus for testing same|
|US20040183571 *||Jan 29, 2004||Sep 23, 2004||Gunter Marzinger||Circuit arrangement having a phase detector and phase locked loop including the circuit arrangement|
|US20080088351 *||Sep 19, 2007||Apr 17, 2008||Nec Electronics Corporation||Phase shifting circuit|
|US20110025387 *||Mar 4, 2009||Feb 3, 2011||Cambridge Silicon Radio Limited||Charge Transfer in a Phase-Locked Loop|
|CN1741389B||Aug 26, 2004||Jun 11, 2014||瑞昱半导体股份有限公司||Phase-locked loop with nonlinear phase error response characteristics|
|DE4342344A1 *||Dec 11, 1993||Jun 14, 1995||Telefunken Microelectron||Circuitry for PLL with phase detector and reference current source|
|DE19515218A1 *||Apr 28, 1995||Oct 31, 1996||Thomson Brandt Gmbh||Oscillator arrangement tuning method|
|DE19935905A1 *||Jul 30, 1999||Feb 8, 2001||Motorola Inc||Electric filter has condenser and control unit that varies charge energy magnitude during charging period; magnitude of change is determined by higher order charge delays of capacitor|
|WO1998010520A2 *||Aug 21, 1997||Mar 12, 1998||Philips Electronic N.V.||Frequency synthesis circuit having a charge pump|
|WO1998010520A3 *||Aug 21, 1997||May 22, 1998||Philips Electronic N V||Frequency synthesis circuit having a charge pump|
|U.S. Classification||327/157, 327/244, 331/1.00A, 331/25, 331/17|
|International Classification||H03L7/089, H03L7/183, H03L7/095, H03L7/107|
|Cooperative Classification||H03L7/0898, H03L7/095, H03L7/183, H03L7/107|
|European Classification||H03L7/107, H03L7/095|
|Aug 21, 1991||AS||Assignment|
Owner name: AMERICAN TELEPHONE AND TELEGRAPH COMPANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:NAGARAJ, KRISHNASWAMY;SHARIATDOUST, REZA S.;REEL/FRAME:005820/0352
Effective date: 19910820
|Sep 30, 1996||FPAY||Fee payment|
Year of fee payment: 4
|Sep 28, 2000||FPAY||Fee payment|
Year of fee payment: 8
|Oct 19, 2004||FPAY||Fee payment|
Year of fee payment: 12
|Nov 15, 2004||AS||Assignment|
Owner name: AGERE SYSTEMS INC., PENNSYLVANIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:AT&T CORP.;LUCENT TECHNOLOGIES INC.;REEL/FRAME:015980/0375;SIGNING DATES FROM 19960329 TO 20010130